Single element typewriters have historically utilized a rotating shaft to effect cam rotation. The shaft either carried with it a single cam with a plurality of cam grooves, each individually selectable by its own cam follower, such as that found in Shakib, U.S. Pat. No. 3,892,304, or a single cam groove was formed into a rotating shaft with a form of a relievable follower assembly attached driveably to that cam groove as in DeKler, U.S. Pat. No. 3,983,984 and Hughes, U.S. Pat. No. 4,094,397. The rotation of the shaft to provide the movement of a cam in its simplest form will provide only a single defined mechanical output absent a plurality of cam surfaces or a motion modifying device. The DeKler and Hughes patents provide an alternative to multiple cam surfaces but utilized a fixed cam drive. The fixed cam drive must be defined in such a way that the cam rise is fast enough to accommodate the greatest possible amount of selection movement required of the type element and, therefore, must generate higher than required accelerations and forces during many of the printing and selection cycles of the typewriter. It is desirable to overcome the high loading conditions and reduce accelerations and forces generated during the selection cycle. The avoidance of high loading and accelerations on the drive system of the typewriter may be accomplished by multiple cam surfaces as the prior art has implemented, but the requirement of extensive adjustments and the multiplication of parts makes the manufacture of the apparatus more complicated and expensive.
Another example of a multiple cam surface selection apparatus is Schaefer, U.S. Pat. No. 3,666,070 where face cam surfaces are formed conically into a cam cylinder. Cam profiles are expensive to design and to manufacture in materials which will withstand high stresses and, therefore, increase the expense of such a typewriter.
The DeKler patent referred to above discloses a spring biased detent ball acting as a cam follower in a continuing cam groove to translate a follower block into forceable engagement with a controllable and selectable stop member. The detent ball relieves forces of the cam groove against the follower block when the follower block has forceably engaged the increment defining interposers. An alternative and improved approach which reduced forces and stresses involved in driving the selection system is disclosed in the Hughes patent where a follower block riding in a shuttle engages a stop member and then is spring relieved to provide a capability of driving the shuttle through the remainder of its movement while stopping the typehead movement defining linkage attached to the individual follower blocks.
The DeKler and Hughes devices, while both driving the rotate linkage only so far as needed for selection, must accommodate high acceleration and deceleration forces during the early portion of a print cycle regardless of the amount of rotation of the typehead desired and, therefore, is subjected to unnecessarily high forces during many of the selection cycles. The Schaefer patent, although not requiring excessive acceleration and loading of the selection system during the cycles selecting relatively close or low rotate value characters, requires a more complex cam with concomitant design and manufacturing problems.
The variable cam profile selection system disclosed herein utilizes two ring members pivoted on collars mounted on a print shaft capable of rotation in a cyclic manner. The annular ring cam surfaces are thus able to pivot with respect to these collars, thereby presenting to the cam follower engaged therewith, a cam rise of controlled but variable height. By controlling the height with a mechanical device such that the height of the cam rise corresponds to the input increment required to control the rotation of the type element for a desired quantity of element rotation and likewise element tilt, the mechanical displacement of the followers may be translated from the variable cam profiles to varying but controlled rotation and tilt increments of the typehead. The amount of cam rise is controlled by the removal of interposers from a zone of engagement with a stop member and a moveable cam control slide surface. If all interposers are left in the zone of engagement, the cam will exhibit its highest rise while with each additional removal of interposers, the cam rise will diminish. The interposers are extracted prior to the initiation of a selection cycle and remain extracted from the zone of engagement until the completion of the selection cycle and the restoration of the cam member and the cam slide.
In summary, the invention is a unitary cam member capable of movement under control of a selectable apparatus to be positioned, thereby providing a plurality of cam rises from a single cam member.